1. Field of the Invention
The present invention relates to compressors that are used in vehicle air conditioners. More particularly, the present invention pertains to sliding structure of pistons in a compressor.
2. Description of the Related Art
A typical compressor used in a vehicle has the following construction. The compressor includes a housing, and a cylinder block constitutes a part of the housing. A crank chamber is defined in the housing. A drive shaft is rotatably supported in the crank chamber. The cylinder block has cylinder bores formed therein. A piston is reciprocally housed in each cylinder bore. A cam plate is supported on and rotates integrally with the drive shaft in the crank chamber. Each piston is connected to the cam plate by means of shoes. Rotation of the drive shaft is converted into linear reciprocation of the pistons by the cam plate. Refrigerant gas in the cylinder bores is compressed by the reciprocation.
In such a compressor, the inertial force acting on each piston becomes greatest when the piston shifts from the suction stroke to the compression stroke. The inertial force of the piston acts on the cam plate. On the other hand, the piston receives a reaction force from the cam plate. The reaction force includes a lateral component that is directed radially outward from the axis of the cam plate. This component presses a part of each piston head against the inner wall of the associated cylinder bore. This lateral component of the reaction force will be referred to as the lateral force. The inertial force of the pistons increases as the weight of the piston is increased. An increased inertial force of the pistons results in a greater lateral force acting on each piston.
However, the housing, which includes the cylinder block, and the pistons are made of aluminum alloy, which is light, for reducing the weight of the compressor. Therefore, when a piston is reciprocating in the associated cylinder bore, the above described lateral force prevents the piston from smoothly sliding with respect to the cylinder bore.